Pressure relief system

ABSTRACT

A pilot operator for controlling main valve operation to relieve overpressure from a system to which the main valve is connected. A spring biased pilot disc normally maintains the operator closed in opposition to system pressures below set pressure. On an overpressure being encountered, the disc lifts from its seat to effect main valve operation. A variably presettable adjustment in the path of disc movement regulates lift distance for effecting desired blowdown operation of the main valve.

United States Patent [191 Ferrill June 11, 1974 PRESSURE RELIEF SYSTEM [75] Inventor: Homer E. Ferrill, Alexandria, La. Pnmary *l K k Attorney, Agent, or Firm-Daniel Rubm [73] Assignee: Dresser Industries, Inc., Dallas, Tex. [22] Filed: Aug. 15, 1973 57 ABSTRACT pp 388,687 A pilot operator for controlling main valve operation Related Us. Application Data to relieve overpressure from a system to which the [63] Continuation of ser No 224 862 Feb 9 [972 main valve s connected. A spring biased pilot disc normally mamtams the operator closed 1n opposition to system pressures below set pressure. On an over- 2% ga 137/4925; pressure being encountered, the disc lifts from its seat d 5 510 478 to effect main valve operation. A variably presettable I o are adjustment in the path of disc movement regulates lift distance for effecting desired blowdown operation of [56] References Cited the main valve 7 UNITED STATES PATENTS 7/l969 Buresh et al 137/4925 X 8 Claims, 5 Drawing Figures PATENTEDJUNI 1 I974 SHEEI 2 Bf 3 PRESSURE RELIEF SYSTEM Cross-References to Related Applications This is a continuation of application Ser. No. 224,862 filed Feb. 9, I972, now abandoned.

BACKGROUND OF THE INVENTION 1. The field of art to which the invention relates include the art of Fluid Handling" as contained in Patent Office classification 13L 2. The majority of safety valves in use for steam service and the like are self-contained units directly responsive to system pressures for relieving overpressure when required. For large capacity requirements, it is fairly common to employ a relatively small pilot valve that is responsive to system pressure for controlling operation of the main valve through which relief is effected. This arrangement has a principal advantage for large capacity requirements in affording a substantial reduction in main valve size enabling a more economic choice of operating-components while substantially reducing the space requirements otherwise needed for installation of the valve.

Associated with these valves of either type is the operating performance factor referred to as blowdown, being the difference between set pressure and closing pressure measured as a percentage of set pressure. For reasons known in the art, as for example discussed in US. Pat. No. 3,401,718, capacity performance of the valves is inversely related to the blowdown factor. Consequently, most valves, as a practical matter, are constructed to provide a tolerable compromise between capacity and blowdown operation. At the same time,

many customers of such valves have their individual needs because of their own peculiar circumstances related to the particular application in which the valves are to be utilized. Rather than accept-an advance factory determined blowdown characteristic of the valves, the customers prefer to regulate or preset blowdown, even onsite, as a function of their own operating requirements. Whereas adjustment for varying blowdown operation has been known for safety valves of the selfcontained type, it has not heretofore been known how to presettably adjust a pilot operator for regulating blowdown operation of the main valve being controlled thereby.

SUMMARY This invention relates to safety valves. More particularly, this invention relates to pilot operators for controlling a main safety valve to effect relief of system overpressure to which the valve is connected. By a presettable adjustment feature in the pilot operator blowdown operation of the main valve can be varied within a wide percentage range for meeting different purchaser operating requirements. This is achieved in accordance with the invention by means of an adjustment that presettably regulates the extent of lift incurred by the pilot disc in response to an encountered system overpressure. Increasing the extent of permitted lift decreases blowdown and vice versa affording each individual purchaser the ability to operate the valve at a blowdown condition of his choice. Consequently, by means of a relatively simple construction feature on a pilot operator, the prior longstanding inability to regulate blowdown via the pilot has been readily resolved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of the pilot and actuator valves assembled to the main valve shown sectioned;

FIG. 2 is a sectional elevation taken substantially along the lines 2-2 of FIG. 1;

FIG. 3 is a fragmentary section schematically illustrating the operable flow connections between the pilot, actuator and main valves of the assembly;

FIG. 4 is an enlarged sectional elevation through the.

pilot operator in accordance herewith illustrated in its closed relation; and

FIG. 5 is afragmentary section of the pilot operator similar to'FIG. 4 but illustrated in its open relation.

The operating structure to which the invention relates will first be described with reference to the drawings illustrating an assembly principally intended for use on large capacity steam service or the like with system pressures on the order of 1,999 PSI and above. The assembly, as will be briefly described, comprises a main valve 10 secured via an intermediate block 13 to an actuator valve 30 and a juxtaposed pilot operator in accordance herewith designated 50. 1

Main valve 10, by which system overpressure is ultimately relieved, is best seen in FIG. 1 and comprises a body 11 having a flanged bottom connection 12 for mounting onto a piping system with which the valve is to be utilized. An inlet passage 14 receives the high pressure system fluid, generally steam, from where it disburses through a flow constriction l5 surrounding the main valve disc 16. The disc includes an annular cavity about its left side (as viewed in the drawings) receiving a compressed coil spring 18 urging the disc against annular seat 19 leading to outlet discharge passage 21. A plurality of small diameter drainage ports 22 connect inlet passage 14 with cavity 17 for supplying inlet pressure to back pressure chamber 23. Pressure from the chamber is in turn communicated via conduit 29 (FIG. 3) to actuator 30. Also receiving system pressure from inlet 14 is a sensing tube 25 which via conduit 26 in top flange 27 communicates inlet pressure to pilot operator 50. Conduit 28 provides for discharge from the actuator as will be described. When main 'valve 10 is to be opened for pressure relief, disc 16 moves leftward into chamber 23 under axial guidance of cylindrical guide pin 24 exposing inlet 14 to discharge outlet 21.

Actuator 30, as best seen in FIG. 2, comprises a base 31 having a vertically central passage 32 containing the essential operating componentsand is closed at its bottom side by means of a cover plate 33. Among the latter components is a piston 34 compressing a coil spring 35 against an actuator seat 36. At the central underside of the piston aboss 38 secures a vertically slideable spindle 39 supporting an actuator disc 41. A transverse passage 44 exposes the top of piston 34 to the output discharge of pilot operator 50 for effecting downward movement of the spindle. The latter movement results in uncovering of ports 42 and 43 communicating with main valve passages 28 and 29 respectively (FIG. 3). An air diaphragm arrangement 45 provides auxiliary means for operating actuator 30 when required.

Pilot actuator 50, as shown in FIGS. 2-6, comprises a hollowed base section 51 closed on its bottom side by a cover plate 53. Inlet system pressure supplied through conduit 26 is received via a port 52 into a lower chamber 54 from which it disburses upwardly through a central bore 55 in an annular seat bushing 56. The top radial face of bushing 56 defines an annular seat 60 with which an axially moveable disc 61 cooperates for opening and closing passage 55. Urging the disc into seating engagement in opposition to inlet pressure is a spindle 62 biased downwardly by means of a compressed coil spring 63. An outlet chamber 64, surrounding the disc, connects via a plurality of vertical ports 65 with connecting actuator passage 44. When disc 61 lifts or is elevated to the relation of FIG. 5 in response to a system overpressure in passage 55 reacting against the primary seat area of the disc, fluid thereat discharges into passage 44 to sequentially initiate actuator and main valve operation.

As thus far described, operation of the assembly, which should be understood for better appreciation of the invention, is dependent on the magnitude of system pressure received at inlet 14. Fluid at system pressure received thereat fills the interior of passage 14 up to seat 19 and through drainage holes 22 fills chamber 23. From the chamber, pressure is communicated via passage 29 to port 43 to the underside of actuator disc 41. System pressure in chamber 23 aided by spring 18 maintains disc 16 in its closed seated relation. At the same time, inlet pressure is transmitted by sensing tube 25 and conduit 26 into passage 55 to the underside of disc 61.

Upon reaching set pressure of pilot operator 50, as determined in a conventional manner by the preset compression force of spring 63, system pressure reacting on the primary area of pilot disc 61 causes it to raise from its seat. As lift begins, fluid exposure to the increased disc diameter effects full or rated lift of the disc to theposition illustrated in F IG. 5. 1n full lift relation, system fluid flows into chamber 64, port 65 and passage 44 to act downwardly on the top surface of actua tor piston 34. Downward fluid force imposed against the piston displaces its downwardly causing spindle 39 to unseat actuator disc 41. Unseating the latter in tum opens port 43 to reduce the pressure in chamber 23 by discharging that fluid through port 42 to conduit 28 connecting with main valve outlet 21. When chamber pressure is sufficiently reduced, system pressure ac t ig a position closing port 43. System' pressure immediately builds up again in chamber 23 causing the main valve disc to seat and arrest discharge from inlet 14.

With the foregoing in mind, the adjustment feature of the invention for presettably effecting desired blowdown operation of the main valve will now be described with specific reference to FIGS. 4 and 5. For these purposes, the top radial backface of pilot disc 61 includes an annular bevelled rib internally defining the backseat diameter and the apex of which when the disc is at full lift, engages the radial underface of a lift plug 71. In lifting from the closed relation of F IG. 4 to the open relation of FIG. 5, the disc path of travel is over a movement distance designated X.

Plug 71 is bored at 72 to coaxially encircle spindle 62 with sufficient clearance to enable fluid communication with vent 66. The plug is supported threaded in cover plate 73 such that by threadedly advancing it toward and away from the closed position of disc 61,

the lift distance X can be presettably adjusted to a. choice setting within the available range. Once the detributed about the plug circumference. The spacing between notches is correlated to a known axial plug displacement such that a change in setting of the lift distance X can be readily effected by counting the rotational notch displacement from one pin setting to another. Preferably, for convenience of reference, notch counting is from a zero position in touching engagement against rib 70 of the closed disc.

The significance of altering lift distance X for effecting blowdown'operation can perhaps best be appreciated by considering the following exemplary comparative calculations. Assume the following operating conditions and construction features applied to a pilot operator in accordance therewith:

With the foregoing constant, changes in the lift setting distance X produces correlated blowdown changes as follows:

Notches From Touching Lift X inches 0.0416 0.04368 0.04784 Additional Spring Load lbs. 222.56 233.69 255.94

Total Spring Load When Back l.04 9l2.l7 934.42

Seated lbs.

Pressure at onset of valve 1147.09 1161.26 H8959 closing PSI Blowdown From the above comparison, it can be seen that blowdown is inversely related to the lift distance, i.e., the greater the lift distance X, the smaller the blowdown and vice versa. To operate the pilot controller at any desired blowdown therefore requires the mere threaded adjustment of plug 71 whereby to variably regulate the extent of total lift of disc 61 from its closed relation of FIG. 4 to its open relation of FIG. 5.

By the above description there has been disclosed novel apparatus for presettably adjusting a pilot operator to regulate and control desired blowdown operation of an associated main valve pursuant to individual customer requirements. The adjustment structure of the invention is simple and inexpensive to manufacture, yet is highly effective in rendering this adjustment feature available in overcoming a long standing problem of providing main valve blowdown adjustment via the pilot operator.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the drawings and specifications shall be interpreted as illustrative and not in a limiting sense.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A pressure relief system for high pressure steam service comprising in combination:

a. a main valve including:

l. body meansdefining a main valve passage having an inlet adapted to be connected with a source of steam service from which relief is to be effected and an outlet for discharging overpressure from said source;

2. a moveable closure disc positioned intermediate the inlet and outlet of said main valve passage for opening and closing said passage to fluid flow from said source;

3. spring means biasing said closure disc toward closed position in opposition to source pressure at the inlet of said main valve passage; and

4. means defining a back pressure chamber in constant communication with source pressure at said inlet for pressure therein to aid said spring means in biasing said closure disc toward said closed position;

b. an actuator valve operably connected to said main valve and including:

1. body means defining an actuator passage having an inlet in communication with the back pressure chamber of said main valve and an outlet in communication with the outlet of said main valve passage; and

2. piston means in said actuator passage operably moveable between positions to open and close said passage to fluid flow; and

c. a pilot operator including:

1. body means defining a pilot passage having an inlet adapted to be connected with the same source of steam service to which the main valve passage is connected and an outlet for discharging overpressure from said source;

2. disc means in said pilot passage operably moveable between positions to open and close said passage to fluid flow;

3. spring means biasing said disc means toward closed position in opposition to source pressure at the inlet of said pilot passage;

4. said pilot passage outlet being in communication with the piston means of said actuator valve for enabling fluid pressure when present in saidoutlet to operate said actuator piston means to the open position of said actuator passage whereby to effect concomitant movement of said main valve closure disc to the open position of said main valve passage; and

5. adjustment means effective to variably preset main valve blowdown in response to relief operation of fluid pressure from said source.

2. A pressure relief system according to claim 1 in which said pilot operator adjustment means comprises means to presettably regulate the distance limits of said pilot operator disc means in moving between its said closed and full open positions in said passage.

3. A pressure relief system according to claim 2 in which said pilot operator adjustment means settings of said distance limits are inversely related to the effected main valve blowdown operation.

4. A pressure relief system according to claim 3 in which said pilot operator adjustment means comprises means to presettably vary the total lift distance of said pilot operator disc means in moving to said open position against the force of said spring means.

5. A pressure relief system according to claim 4 in which said pilot operator adjustment means comprises an axially moveable plug coaxially aligned with said pilot operator disc means and supported in interfering relation in the path of disc means movement for defining the disc means lift limit in its full open position. 6. A pressure relief system according to claim 5 in which said plug is threadedly supported and includes external indicia referencing the threaded lift distance setting thereof.

7. A pressure relief system according to claim 6 in which said pilot operator disc means includes a protuberance axially extending toward the proximate surface of said plug for engagement therewith at said full open position to define the open limit of said disc means lift.

8. A pressure relief system according to claim 7 in which said protuberance comprises an annular bevel having an apex adapted to engage the proximate surface of said plug. 

1. A pressure relief system for high pressure steam service comprising in combination: a. a main valve including:
 1. body means defining a main valve passage having an inlet adapted to be connected with a source of steam service from which relief is to be effected and an outlet for discharging overpressure from said source;
 2. a moveable closure disc positioned intermediate the inlet and outlet of said main valve passage for opening and closing said passage to fluid flow from said source;
 3. spring means biasing said closure disc toward closed position in opposition to source pressure at the inlet of said main valve passage; and
 4. means defining a back pressure chamber In constant communication with source pressure at said inlet for pressure therein to aid said spring means in biasing said closure disc toward said closed position; b. an actuator valve operably connected to said main valve and including:
 1. body means defining an actuator passage having an inlet in communication with the back pressure chamber of said main valve and an outlet in communication with the outlet of said main valve passage; and
 2. piston means in said actuator passage operably moveable between positions to open and close said passage to fluid flow; and c. a pilot operator including:
 1. body means defining a pilot passage having an inlet adapted to be connected with the same source of steam service to which the main valve passage is connected and an outlet for discharging overpressure from said source;
 2. disc means in said pilot passage operably moveable between positions to open and close said passage to fluid flow;
 3. spring means biasing said disc means toward closed position in opposition to source pressure at the inlet of said pilot passage;
 4. said pilot passage outlet being in communication with the piston means of said actuator valve for enabling fluid pressure when present in said outlet to operate said actuator piston means to the open position of said actuator passage whereby to effect concomitant movement of said main valve closure disc to the open position of said main valve passage; and
 5. adjustment means effective to variably preset main valve blowdown in response to relief operation of fluid pressure from said source.
 2. a moveable closure disc positioned intermediate the inlet and outlet of said main valve passage for opening and closing said passage to fluid flow from said source;
 2. disc means in said pilot passage operably moveable between positions to open and close said passage to fluid flow;
 2. piston means in said actuator passage operably moveable between positions to open and close said passage to fluid flow; and c. a pilot operator including:
 2. A pressure relief system according to claim 1 in which said pilot operator adjustment means comprises means to presettably regulate the distance limits of said pilot operator disc means in moving between its said closed and full open positions in said passage.
 3. A pressure relief system according to claim 2 in which said pilot operator adjustment means settings of said distance limits are inversely related to the effected main valve blowdown operation.
 3. spring means biasing said disc means toward closed position in opposition to source pressure at the inlet of said pilot passage;
 3. spring means biasing said closure disc toward closed position in opposition to source pressure at the inlet of said main valve passage; and
 4. said pilot passage outlet being in communication with the piston means of said actuator valve for enabling fluid pressure when present in said outlet to operate said actuator piston means to the open position of said actuator passage whereby to effect concomitant movement of said main valve closure disc to the open position of said main valve passage; and
 4. means defining a back pressure chamber In constant communication with source pressure at said inlet for pressure therein to aid said spring means in biasing said closure disc toward said closed position; b. an actuator valve operably connected to said main valve and including:
 4. A pressure relief system according to claim 3 in which said pilot operator adjustment means comprises means to presettably vary the total lift distance of said pilot operator disc means in moving to said open position against the force of said spring means.
 5. adjustment means effective to variably preset main valve blowdown in response to relief operation of fluid pressure from said source.
 5. A pressure relief system according to claim 4 in which said pilot operator adjustment means comprises an axially moveable plug coaxially aligned with said pilot operator disc means and supported in interfering relation in the path of disc means movement for defining the disc means lift limit in its full open position.
 6. A pressure relief system according to claim 5 in which said plug is threadedly supported and includes external indicia referencing the threaded lift distance setting thereof.
 7. A pressure relief system according to claim 6 in which said pilot operator disc means includes a protuberance axially extending toward the proximate surface of said plug for engagement therewith at said full open position to define the open limit of said disc means lift.
 8. A pressure relief system according to claim 7 in which said protuberance comprises an annular bevel having an apex adapted to engage the proximate surface of said plug. 